The Dutchman grabbed his first from Momo Sylla's superb cross and made it 2-0 when Elvis Hammond's mis-timed volley landed straight at his feet.
Lee Peacock's effort was tipped over by Rab Douglas and David Graham's shot hit the post as the Owls improved.
But Stephen Hughes twice went close to sealing victory before Douglas made a fantastic save from Peacock's header.
Sheff Wed boss Paul Sturrock:
"We're not a great passing team - we've never been once since I came here.
"When we play square and back we cause ourselves all sorts of concern.
"I don't expect us to play it long but I expect us to be penetrative. Sooner or later - through selection or a penny dropping - they'll come into line."
Leicester: Douglas, Maybury, Johansson, Dublin, Sheehan, Sylla (Wilcox 88), Gudjonsson, Williams, Hughes (Kisnorbo 78), Hammond (Hume 77), de Vries.
Subs Not Used: Henderson, McCarthy.
Goals: de Vries 10, 12.
Sheff Wed: Lucas, Simek, Wood, Coughlan, Ross (Corr 79), Eagles, Whelan, Rocastle (Brunt 68), O'Brien, Peacock, Graham (Bullen 68).
Subs Not Used: Adamson, Lee.
Booked: Rocastle, Whelan.
Ref: G Sailsbury (Lancashire).